Input distribution in MadGraph

Asked by Maksym Ovchynnikov on 2021-03-22

Consider a particle X that decays into some SM particles. This part may be easily incorporated in MadGraph. Consider a case when X is produced in decays of some particle (say, B-meson) that are not incorporated (and may not be incorporated) in MadGraph. Let us assume however that we have a distribution of X from some side calculations.

Is it possible to modify MadGraph in a way such that instead of generating events with X in MadGraph

p p > X, X > ...

we just generate

X > ...,

but provide the X spectrum as an input to MadGraph?

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Last query:
2021-03-26
Last reply:
2021-03-26

Hi,

It actually depends of what you want to do and which effects you want to include.

If you do not care about width effect and about spin-correlation, then
you can generate
> X > ...,
and then boost event by event your event according to your distribution
This is actually what madspin is doing in the "spinmode=none" mode.

We also have such type of mode for hepmc input (see the maddump paper).

Cheers,

Olivier

> On 22 Mar 2021, at 10:35, Maksym Ovchynnikov <email address hidden> wrote:
>
> New question #696182 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/696182
>
> Consider a particle X that decays into some SM particles. This part may be easily incorporated in MadGraph. Consider a case when X is produced in decays of some particle (say, B-meson) that are not incorporated (and may not be incorporated) in MadGraph. Let us assume however that we have a distribution of X from some side calculations.
>
> Is it possible to modify MadGraph in a way such that instead of generating events with X in MadGraph
>
> p p > X, X > ...
>
> we just generate
>
> X > ...,
>
> but provide the X spectrum as an input to MadGraph?
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Maksym Ovchynnikov (name-xxx) said : #2

Thanks Olivier! Does the mentioned syntax > X > ... assume that the X particle is at rest?

Maksym Ovchynnikov (name-xxx) said : #3

Also, I tried to run

generate > V > chi chi~

in MadGraph (V, chi, chi~ are new physics particles), but it said that "InvalidCmd : "> V > chi chi~" is a wrong process format. Please try again". What I made wrong there?

You have to do
generate V > chi chi~

Sorry the indentation of the email added a ">" that confuse you

Cheers,

Olivier

Maksym Ovchynnikov (name-xxx) said : #5

Hi again,

may I please ask you to clarify the following:

"This is actually what madspin is doing in the "spinmode=none" mode. We also have such type of mode for hepmc input (see the maddump paper)."

Does it mean that MadDump may use as an input a hepmc file with the spectrum and follow the procedure that you have described?

"If you do not care about width effect and about spin-correlation, then
you can generate
> X > ...,
and then boost event by event your event according to your distribution"

Yes,

Maddump can indeed take an hepmc as input and decay the pion/Kaon spectrum in that way.

Cheers,

Olivier

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